A low reflection coating is sometimes formed on the surface of a glass or ceramic substrate in order to allow transmission of more light or prevent glare caused by reflection of light and thus to improve the function of the substrate for a specific application.
Glass sheets provided with low reflection coatings are used in vehicle windows, shop windows, photoelectric conversion devices, etc. In a thin-film solar cell as a type of photoelectric conversion device, an undercoating film, a transparent conductive film, a photoelectric conversion layer made of amorphous silicon or the like, and a thin-film back electrode are stacked in this order on one principal surface of a glass sheet, and a low reflection coating is formed on the other principal surface of the glass sheet opposite to the one principal surface. In a crystalline solar cell as another type of photoelectric conversion device, a low reflection coating is formed on the surface of a cover glass disposed on the sunlight incident side. In a solar cell, a low reflection coating is formed on the sunlight incident side as described above, more sunlight is directed to a photoelectric conversion layer or a solar cell element, and thus the amount of electricity generated in the cell is increased.
A most frequently used low reflection coating is a dielectric film formed by vacuum deposition, sputtering, chemical vapor deposition (CVD), or the like. A fine particle-containing film containing fine particles such as fine silica particles is also used as the low reflection coating in some cases. The fine particle-containing film is formed by applying a coating liquid containing the fine particles onto a glass sheet by dip coating, flow coating, spray coating, or the like.
When a fine particle-containing film as a low reflection coating is formed by spray coating, the appearance may significantly deteriorate due to uneven reflection. In order to reduce such deterioration in appearance, for example, WO 2011/070714 A1 (Patent Literature 1) discloses a cover glass for photoelectric conversion devices that includes a glass sheet and a reflection-reducing film (low reflection film) containing fine silica particles, in which the shape of the surface asperities of the glass sheet and the number of layers of the fine silica particles stacked in the peak portions of the surface asperities and that in the valley portions of the surface asperities are adjusted. This cover glass has a reflectance of 1.5% or more and 3% or less over the entire wavelength range of 380 nm to 780 nm for light incident on the reflection-reducing film formed on the glass sheet, and thus the deterioration in appearance due to uneven reflection is reduced.